American journal of physiology. Cell physiology最新文献

Mutations in the gene encoding the skeletal muscle ryanodine receptor (RyR1) can result in muscle diseases, termed RyR1-related myopathies (RyR1-RM). Examples include malignant hyperthermia (MH), central core disease (CCD), and centronuclear myopathy (CNM). The muscles involved often have more (and mispositioned) nuclei than normal. A subset of the corresponding mutant proteins shows an overactive or leaky sarcoplasmic reticulum (SR) channel behavior that depletes the SR Ca²⁺ content and increases the level of cytosolic Ca²⁺. In addition, two remarkable effects of these RyR1 variants have been reported in cultured myogenic cells: enhanced expression of interleukin-6 (IL-6) and stimulation of myoblast fusion (myonuclei accretion). Here, we have investigated whether the latter effect is due to a possible IL-6-dependent autocrine loop. Toward this goal, we analyzed the impact of the overactive Y523S mutant compared with the wild-type RyR1 after expression in C2C12 cells. The results show that this mutation indeed drastically promotes myoblast fusion up to ∼300%. Moreover, this action depends on the sequential activation of SR Ca²⁺ release, store-operated Ca²⁺ channels, reactive oxygen species (ROS, cytosolic and mitochondrial), calpain, and calcineurin. In addition, a neutralizing antibody directed against IL-6 and a p38 inhibitor completely suppressed the stimulation of myoblast fusion. Furthermore, in RyR1-expressing cells, myotube formation was promoted by either exogenous IL-6 or conditioned medium obtained from the Y523S-expressing cells. These findings suggest an autocrine mechanism involving the interplay between Ca²⁺, ROS, IL-6, and p38 signaling pathways in controlling myonuclei density, which could be essential to explain the pathogenesis of RyR1-RM.NEW & NOTEWORTHY Overactive RyR1 mutant proteins are associated with muscle disease; interestingly, they increase the number of myonuclei when expressed in C2C12 cells. We discovered that this alteration depends on a Ca²⁺/ROS loop, which recruits calpain and calcineurin to stimulate the production of IL-6 and the subsequent autocrine activation of p38. Thus, disease-causing RyR1 mutations require an IL-6 autocrine system to alter myonuclear density. This novel mechanism could be critical to understanding the pathogenesis of congenital myopathies.

White and brown adipose tissues are organized to form a true organ. White adipose tissues store energy that is provided to the organism in the intervals between meals and brown adipose tissues burn lipids to produce heat. When the cold exposure is chronic, white converts into brown (browning) to help thermogenesis and when the energy balance is chronically positive, brown converts into white (whitening) to help store energy. The plastic property of the adipose organ also allows a reversible formation of milk-producing alveolar cells in the mammary fat during pregnancy and lactation (pinking, because the organ is pink during pregnancy). This last striking property of the adipose organ is challenged by other authors, but our data, based on morphology (including electron microscopy), immunohistochemistry, lineage tracing, explants, and in vitro data described here, support this phenomenon. Our experiments, including microarray data comparing cleared fat pad with normal glands in pregnant mice, allowed us to detect four molecular players in the pinking phenomenon: E74-like ETS transcription factor (ELF5), osteopontin, GATA binding protein 3 (GATA3), and Mir200c. Another molecular player could be the parathyroid hormone-related protein (PTHrP). Mice lacking each of these molecules have impaired alveologenesis during pregnancy. Finally, several data seem to suggest a strong functional relationship between the onco-suppressor gene breast cancer gene 1 (BRCA1) and the reversible adipo-epithelial transdifferentiation phenomenon, opening new avenues for future studies in the connection between pinking and breast cancer.

The prevalence of heart failure (HF) and of chronic kidney disease (CKD) is continuously rising. Both diseases require significant management efforts, and more importantly, HF is often associated with CKD, aggravating the clinical scenario and leading to "cardiorenal syndrome" (CRS). Although clinical studies suggest a bidirectional interaction between HF and CKD, the pathophysiological understanding of CRS remains incomplete. Several mechanisms are involved in CRS, including changes in systemic and renal hemodynamics, endothelial dysfunction, inflammation, and activation of the renin-angiotensin-aldosterone and sympathetic nervous systems. However, the precise mechanisms are still unclear, partly because of the incomplete characterization of experimental models recapitulating CRS. In this review, we analyze recent studies using different animal models of CRS, such as primary HF, primary CKD, and the "double-hit" models that have been proposed to investigate the pathophysiology of this condition. In HF models, data on renal pathology showed renal fibrosis, inflammation, and decreased glomerular filtration rate (GFR), whereas kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) were used as markers of early kidney damage. In CKD models, data on heart pathology indicated changes in hemodynamics, increased systolic blood pressure, and the presence of fibrosis. These models provide new insights into the pathophysiological development of CRS, particularly the "double-hit" models, which may offer more information about the cross talk between the heart and kidneys. This review emphasizes the complexity of CRS and highlights the need for further research to clarify the underlying interactions and mechanisms.

At the neuromuscular junction, nicotinic acetylcholine receptor (nAChR) dynamics are regulated in a nerve- and activity-dependent manner. Correlated local alterations in myoplasmic [Ca²⁺]_i, induced by IP₃-sensitive subsynaptic Ca²⁺ stores, have been proposed to signal motor endplate adaptation to motor neuron stimulation. Accordingly, there is evidence for a modulatory role of Ca²⁺/calmodulin-dependent protein kinase IIβ (CaMKIIβ) in the sorting, targeting, and/or incorporation of nAChRs into the postsynaptic membrane. As the scaffold protein Homer 2 emerges as a key player in integrating downstream postsynaptic signaling pathways, this study investigated the possible involvement of Homer 2 in the molecular mechanism controlling nAChR dynamics. Using Homer 2^-/- transgenic mice, it was found that Homer 2 ablation leads to a chronic adaptation of the endplate characterized by: 1) reduction in nAChR activity due to slower insertion of nAChRs into the endplate; 2) reduced subsynaptic IP₃R1 content and IP₃-releasable Ca²⁺; and 3) impaired colocalization of CaMKIIβ with nAChRs. Overall, the present results demonstrate that Homer 2 ablation produces a significant alteration in endplate nAChR dynamics, which is associated with impaired organization of the subsynaptic IP₃-driven Ca²⁺ signaling mechanism.NEW & NOTEWORTHY This research sheds light on the role of Homer 2 in organizing the subsynaptic microdomain, where nAChRs, IP₃R1s, and CaMKIIβ assemble to regulate nAChR dynamics. The present results point to a novel type of endplate instability, which may have implications for understanding neuromuscular junction function and related disorders.

Dysregulation of cholesterol metabolism can lead to obesity and increase the risk of developing many diseases, including type 2 diabetes and cardiovascular diseases. Our previous studies have identified postsynaptic density-95, disc large, and zonula occludens-1 (PDZ) adaptor proteins Na⁺/H⁺ exchange regulatory factor Nherf1 (encoded by Nherf1) and Nherf2 (encoded by Nherf2) to be potential regulators of cholesterol metabolism in vitro. In this study, we explored their physiological regulatory function in vivo by using Nherf1- and Nherf2-deficient (Nherf1^-/- and Nherf2^-/-), and wild-type (C57BL/6) mice. All mice were fed either a chow diet or a cholesterol-enriched Western diet (42% fat, 0.2% cholesterol) for 8 wk starting at 8-wk-old. Our results demonstrate that Nherf2^-/-, but not Nherf1^-/-, mice are resistant to diet-induced obesity. In Nherf2^-/- mice, serum high-density lipoprotein and low-density lipoprotein/very low-density lipoprotein decreased substantially without affecting lipolysis or steroid hormone levels. In addition, distended gallbladders were observed in Nherf2^-/- mice, with reduced bile acid output into the intestine and feces, which correlated with decreased cholesterol reabsorption. This led to attenuated Fxr/Shp signaling in the liver and derepressing Cyp7a1 transcription in the absence of Nherf2. These findings suggest a potential role of in regulating gallbladder emptying and lipid homeostasis, offering new insights into potential therapeutic targets for treating diet-induced obesity.NEW & NOTEWORTHY Nherf2^-/- but not Nherf1^-/- mice demonstrate a resistance to diet-induced obesity. Notably, male Nherf2^-/- mice exhibit impaired glucose tolerance and insulin responsiveness, yet neither sex shows further worsening with diet challenge. In addition, elevated hepatic Cyp7a1 levels were observed in Nherf2^-/- mice, but there was reduced cholesterol absorption in the ileum, along with enlarged gallbladders and diminished ileal bile acid content, highlighting significant metabolic alterations linked to Nherf2 deficiency.

Astrocytes, traditionally viewed as passive support cells, have emerged as critical regulators of neuronal signaling, autonomic function, and cardiovascular homeostasis. Accumulating evidence highlights the active participation of astrocytes in maintaining neurotransmitter balance, ion homeostasis, synaptic plasticity, and cerebral metabolism. In particular, astrocytes form integral components of tripartite synapses, mediating neuronal communication through calcium-dependent release of gliotransmitters, including ATP, glutamate, d-serine, and γ-aminobutyric acid. This astrocyte-mediated signaling is essential in modulating autonomic circuits involved in blood pressure regulation and sympathetic nerve activity. Recent research underscores the role of astrocyte dysfunction-mediated inflammation, termed astrogliosis, in driving pathological states such as hypertension. Astrocyte activation within critical cardiovascular control centers, including the nucleus tractus solitarii, paraventricular nucleus, and rostral ventrolateral medulla, promotes neuroinflammation, disrupts neurotransmitter clearance, and enhances sympathetic nervous system activity. These processes contribute significantly to hypertension development, particularly under conditions of metabolic stress, such as obesity and high-fat diet consumption. Key molecular mechanisms implicated include NF-κB-mediated inflammatory pathways, impaired astrocytic glutamate transporters, overactivation of angiotensin II signaling, and abnormal gliotransmitter release. In this review, we summarize recent advances in our understanding of the physiological roles of astrocytes in autonomic and cardiovascular regulation and discuss the pathological consequences of astrocyte-driven neuroinflammation in hypertension. We further outline promising directions for future research and therapeutic interventions targeting astrocytic pathways, offering potential new strategies for preventing or reversing autonomic dysfunction and hypertension.

Fibrosis plays a crucial role in a range of chronic diseases, including cancer. Emerging evidence suggests that ion channels, transporters, and pumps-the transportome-have an essential share in fibrogenesis and fibrosis by regulating fibroblast and myofibroblast activity. This review bridges current knowledge gaps by integrating insights from multiple diseases affecting the heart, lungs, pancreas, kidney, and liver, as well as cancer. Thereby, we reveal shared molecular mechanisms of how the transportome modulates fibroblast activation, extracellular matrix deposition, tissue stiffness, and remodeling. We focus on the roles of various ion transport proteins, including PIEZO1, transient receptor potential (TRP), K⁺, and cystic fibrosis transmembrane regulator (CFTR) channels; the Na⁺/H⁺ exchanger NHE1; and the Na⁺/K⁺-ATPase. By comparing analogous pathways across different fibrotic diseases such as Ca²⁺ signaling and transforming growth factor β1 (TGF-β1) and Wnt/β-catenin pathways, we highlight the druggable potential of these ion transport proteins and suggest novel concepts for therapeutic intervention.

The diversity of fibroblasts across different organs, and within the same structures, means that their role in both health and disease is manifold. This review focuses on their job in the heart and kidney, specifically during the course of cardiorenal syndrome (CRS). During CRS, there is a complex bidirectional interplay between the two body systems whereby the failure of one drives the decline of the other. These effects manifest by a response that leads to the deposition of fibrotic tissue, attributable to fibroblast dysfunction. Fibroblasts in themselves provide essential functions within organs, which are determined by the specific identity of their subtype. During disease, fibroblast function is further constrained and directed by the niches that form at the sites of injury. This review delves into the origins of fibroblasts in the heart and kidney, their functions in each tissue, and the processes and stressors whereby they become activated to form myofibroblasts. We discuss tools that can be used to study the phenomenon of fibroblast activation in vitro and in human studies and, finally, what therapeutic possibilities there may be in the future.

Resistance training promotes muscle protein accretion and myofiber hypertrophy, driven by dynamic processes of protein synthesis and degradation. Muscle adaptations to ongoing resistance training occur over weeks, but most molecular knowledge on the process of adaptation is derived from static measurements at specific time points, which do not capture the dynamics of the adaptation process. To address this, we utilized deuterium oxide labeling and peptide mass spectrometry to quantify absolute protein content (grams) and synthesis rates (grams/day) in skeletal muscle during a time series experimental design. A daily programmed resistance training regimen was applied to male rat tibialis anterior via electrical stimulation of the left hindlimb for 10, 20, and 30 days (5 sets of 10 repetitions daily). Muscle samples from stimulated and contralateral control limbs were analyzed, quantifying 658 protein abundances and 215 protein synthesis rates. Unsupervised temporal clustering of protein responses revealed distinct phases of muscle adaptation. The early (0-10 days) response was driven by greater rates of ribosomal protein accretion and the mid (10-20 days) response by expansion of mitochondrial networks. These findings highlight that subsets of proteins exhibit distinct adaptation timelines due to variations in translation and/or degradation rates. The new understanding of temporal patterns highlighted by our dynamic proteomic data helps interpret static data from studies at isolated time points and could improve the development of strategies for optimizing muscle growth and functional adaptation to resistance training.NEW & NOTEWORTHY We used stable isotope labeling and proteomic analyses to quantify absolute changes in the synthesis and abundance of muscle proteins during programmed resistance training in rat in vivo. This novel time-resolved approach revealed distinct phases of adaptation, characterized by early ribosomal and later mitochondrial protein accretion. Strikingly, we observed substantial "oversynthesis" of muscle proteins; that is, the net gain in muscle protein content was much less than the amount of newly synthesized protein.

A complication of viral lung infections is the development of pulmonary fibrosis. This phenomenon is most evident in patients with COVID-19, where in its most aggressive form patients developed nonresolvable (NR) COVID-19 requiring lung transplantation. NR-COVID-19 was characterized by the presentation of a fulminant fibrotic lung injury that progressed rapidly, even in patients with limited comorbidities. However, the mechanisms that led to this rapidly progressing form of fibrosis are not fully understood. A common clinical manifestation in the most severe cases of COVID-19 was the presence of "silent" hypoxemia. Thus, we hypothesized that a dysfunctional hypoxic response may result in exacerbated lung injury seen in patients with severe forms of COVID-19. Our results demonstrate that despite increased expression of hypoxia-inducible factor 1A (HIF1A) and its downstream mediator adenosine A_2B receptor (ADORA2B), reduced macrophage HIF1A was observed in patients with severe COVID-19, including NR-COVID-19. Utilizing mice lacking HIF1A in myeloid cells using the lysozyme M Cre promoter, we demonstrate that these mice present with increased lung inflammation and pulmonary fibrosis following chronic low-dose bleomycin treatment. The augmented lung injury was associated with reduced markers for alternatively activated macrophages also observed in NR-COVID-19 lungs. These results point to reduced myeloid HIF1A as a mechanism that can lead to exacerbated lung injury in mice, which parallels the rapid fibrotic response observed in NR-COVID-19. Collectively, our results point to using HIF1A stabilizers as a potential avenue to prevent the development of rapidly progressing postviral lung fibrosis. However, special care is necessary since chronic HIF1A activation is also linked to fibrotic outcomes.NEW & NOTEWORTHY Postviral-induced lung fibrosis represents a severe and potentially fatal outcome. This was most evident during the COVID-19 pandemic, where a subset of individuals presented with fulminant lung fibrosis requiring lung transplantation. The mechanisms that promote this exacerbated lung injury are not fully known. Herein, we demonstrate that mice lacking myeloid hypoxia-inducible factor 1A (HIF1A) develop an exacerbated lung injury response to bleomycin that was consistent with reduced macrophage HIF1A expression in nonresolvable (NR)-COVID-19, characterized by extensive lung fibrosis.